This invention relates to the curing of concrete products, and more particularly to promoting hydration of such products in temperature-controlled, high humidity environments.
Over the years, a number of approaches have been developed for promoting or advancing the curing of concrete products such as piping, slabs, blocks and the like. One common method of curing is to confine concrete products in a totally enclosed room or kiln, and to inject low pressure steam into the kiln from a boiler or steam generator. U.S. Pat. No. 2,622,303 (Wilson) discloses a method for molding double-walled hollow concrete blocks in which nozzles at opposite ends of a mold inject steam into the mold. A multi-stage process is disclosed in U.S. Pat. No. 3,238,279 (Tarlton), including a stage of applying steam alone into a kiln, followed by a mixture of steam and carbon dioxide, and finally a dry air stage.
It also is known to subject the concrete to, steam at high pressure. For example, U.S. Pat. No. 3,957,937 (Lovell) discloses a concrete curing method including subjecting products to superheated steam and carbon dioxide, followed by applications of steam alone, ambient air and cooling air.
Yet another approach involves providing a large trough or body of water at or near the floor of the curing enclosure. In a kiln for curing concrete slabs, U.S. Pat. No. 4,099,337 (Wauhop) shows water being sprayed into a water bath from above, but also from a position below the slabs. The spray is intended to increase evaporation from the bath. U.S. Pat. No. 4,337,033 (Drain) shows a curing system in which the atmosphere inside of the kiln is withdrawn, mixed with a stream of heated water, then injected into a body of water inside the kiln.
All of the above-described methods have a similar objective, namely to supply moisture and raise the ambient temperature of a curing enclosure sufficiently to promote the hydration process. Hydration is an exothermic chemical reaction of cement and water which hardens or solidifies the concrete product during the curing cycle, with the amount of heat generated depending upon the percentage of cement in the product. While the above approaches promote hydration for more rapid curing, they fail to provide uniform and consistent curing necessary for optimum compressive strength. Moreover, systems utilizing steam generators or boilers are expensive to acquire and operate, and, due to the high temperatures involved, subject concrete articles to crusting, baking and hot spotting problems. Bath or trough systems depend upon water vapor and require constant recirculation and heating of the water, and the attendant expensive equipment.
Therefore, it is an object of the present invention to provide a system for curing concrete products at low temperatures compared to steam-based systems and without the use of steam or carbon dioxide.
Another object of the invention is to provide a process for the rapid and uniform curing of concrete articles.
Another object is to provide a low cost system for curing concrete articles in a moderately high temperature atmosphere at or near 100% relative humidity to promote uniform hydration throughout the articles.
Yet another object is to provide a curing process in which, given favorable ambient conditions, the majority of the curing process can be accomplished without providing auxiliary heat.